1. Field of the Invention
The present invention relates to the control of the rotational movement of a disk positioning actuator within a disk storage. More specifically, the invention relates to a rotation assisting mechanism that assists rotation of a rotary actuator so that the actuator is appropriately unloaded with a load/unload (L/UL) mechanism within the hard disk drive when power to the disk drive is turned off.
2. Background Art
FIG. 1 shows a hard disk drive (HDD) 10 which is a disk storage. The HDD 10 is an information storage apparatus making use of (a) a housing 12 which encloses the interior mechanism, (b) at least one rotatable disk 14 with a plurality of concentric data tracks (not shown) each containing information, (c) a magnetic head (not shown) for reading out data from the data tracks or writing data to the data tracks, and (d) a head positioning actuator 20 with the magnetic head at its end for moving the magnetic head to a desired track and supporting it over the desired track during read and write operations. This embodiment has a rotary actuator attached to a spindle 16 (pivot shaft) so that it is rotatable on the spindle 16.
Describing a more specific embodiment, the magnetic head (not shown) includes one or more magnetoresistive (MR) sensors and write transducers. The magnetic head is attached to an air bearing slider 18. The rotation of the magnetic disk creates a thin cushion of air that floats the slider 18 off the data tracks of the disk. The slider 18 is attached to the back surface of the suspension 24 (FIG. 1), and the suspension 24 is connected to an actuator arm 22. The actuator arm 22 is connected to a coil support assembly 40 so that it can be rotated integrally with the coil support assembly. The coil support assembly 40 includes a wire coil 42 which generates a magnetic field when current flows through the wire coil 42 and coil support portions 44 which support the wire coil 42 therebetween.
Two voice coil motor (VCM) magnets 50 are fixed and attached to the side of the housing 12 (one magnet on this side is not shown for viewing), and the magnets 50 constitute part of a VCM which is a motor. When force is developed according to Fleming's law by the relation between the magnetic field present between the magnets 50 and the magnetic field generated when current flows through the wire coil 42, then the actuator assembly 20 and the coil support assembly 40 rotatable integrally with the actuator assembly will be pivoted on the spindle 16.
Various components in the HDD 10 are controlled by control signals generated by a control unit 46. For example, application of current to the coil 42, rotation of the disk 14, and data read and write operations by the magnetic head are controlled by the control unit 46.
The slider 18 is always given a biasing force with respect to the disk surface by the suspension 24, and the biasing force is set so that it is well balanced with a thin cushion of air created by rotation of the disk. The suspension 24 is given flexibility so that the slider 18 is positioned stably and well over the disk being rotated.
Tab 26 extends from the point end of the suspension 24. The entire suspension is a cantilever structure supported at the spindle 16. Therefore, when the tab 26 is supported at the point end, that is, the free end, the handling of the biasing force will be easy. In addition, the deflection of the free end of the suspension can easily be controlled by the tab 26. Furthermore, the slider 18 and the tab 26 are attached at a position near the point end of the suspension, so when tab 26 is supported, the slider 18 can be separated indirectly from the surface of the disk 14. In this embodiment an assembly consisting of the actuator arm 22, suspension 24, and the tab 26 will be called an actuator assembly 20 for the convenience of explanation. This actuator assembly serves as a rotary actuator.
In a load/unload mechanism provided in the HDD 10, the actuator assembly can be moved onto or removed from the disk 14 by controlling the tab 20. In the case where power to the HDD 10 is turned off or when an error occurs and it is desired to end the data read and write operations, the operation of positioning the head over the disk is stopped and an operation of removing or unloading the actuator toward a ramp 30 provided near the outer circumference of the disk is performed. In the unload operation, the actuator assembly 20 is rotated to the ramp 30, and the tab 26 of the actuator assembly 20 is locked in that position until power is restored. When power is restored, a load operation is performed to start a data read operation or a data write operation. In the load operation the tab 26 of the actuator assembly 20 is unlocked from the ramp 30, and the actuator assembly 20 is moved onto the rotating disk.
FIG. 2 is a perspective view showing the ramp 30 that serves as a load/unload mechanism. The ramp 30 is fixed to the housing 12 by use of a support portion 31, for example.
FIG. 3 is a side view of the ramp in FIG. 2 taken substantially along line A--A of FIG. 2, and FIG. 4 is a side view of the ramp in FIG. 2 taken substantially along line B--B of FIG. 2. In this embodiment, four tabs 26 of four actuator assemblies 20 are shown which can be used with two double-sided magnetic disks 14 with data tracks on each disk surface. The final location of the tabs 26 are indicated by broken lines in FIG. 3. Also, the positions of the disks 14 are indicated by broken lines in FIG. 3. The tabs 26 have been given biasing forces (elastic forces) by the suspensions 24 so that they are pressed against the removing surfaces 34a through 34d of the ramp 30, so the tabs 26 can stay at the removing positions. For members with the same configuration, reference characters a through d have been added in sequence after reference numerals to discriminate them from one another. Also, when the suspensions 18 and the sliders 24 are in the removed states, the heads (sliders) are disengaged from the surfaces of the disk 14 and are held, as shown in FIG. 4.
In the case of a load operation, the propulsive force for moving the actuator assembly onto the disk surface can be obtained after power to the HDD is turned on. However, in the case of an unload operation, power supply is stopped, and the actuator assembly must be rotated and moved to the removing position. That is, in order to remove the actuator assembly safely to the removing surface 34a, some energy has to be supplied by an external unit.
In conventional load/unload type HDDs, when power is turned off, the inertial force of the spindle motor rotating the disk 14 is collected and energy required for removal is obtained from this counter electromotive force. More specifically, by causing current to flow through voice coil 42 of a voice coil motor (VCM) with the counter electromotive force, rotational force (torque) is given as assistance to the motor, thereby unloading a rotary type actuator. In order for the unloading of the rotary actuator to succeed, the tab 26 on the point end of the rotary actuator has to slide over the removing place of the ramp 30, particularly the inclinations 33a. Therefore, there is a need to overcome torque which is generated by the friction between the tab 26 and the surface of the ramp 30 (which acts as a resistance to the movement of the tab 26). That is, if the torque given as assistance to the VCM cannot overcome the torque generated by the friction acting as a resistance to the movement of the tab 26, then the rotary actuator cannot reach the final removing position and therefore the removal will not succeed.
If the major factors for removal to succeed are extracted and evaluated, it is found that the following Equation 1 must be satisfied: EQU Kv.times.Ke.times..OMEGA./(Rv+Rm)&gt;F.times.r
where:
Kv=torque constant of the VCM [N m/A]; PA1 Ke=counter electromotive force constant of the spindle motor [V sec/rad]; PA1 .OMEGA.=number of revolutions of the spindle motor [rad/sec]; PA1 Rv=coil resistance of the VCM [ohm]; PA1 Rm=coil resistance of the spindle motor [ohm]; PA1 F=frictional force between the tab on the point end of the suspension and the ramp [N]; and PA1 r=distance from the pivot center of the actuator assembly to the tab on the point end of the suspension [m].
The aforementioned relation can easily be derived if the operation of removing the tab to the ramp is considered. The relation is derived as follows: The counter electromotive voltage of the spindle motor E[V] is represented by E=Ke.times..OMEGA., and the counter electromotive voltage is employed so that current flows through the VCM. Therefore, for the case where the coil of the spindle motor and the coil of the VCM are connected in series, the current l [A] which flows through the coil of the VCM is expressed by l=E/(Rv+Rm). Since the torque T [Nm] of the VCM is expressed by T=Kv.times.l, the left side of Equation 1 is derived as torque which is generated by the VCM when power is turned off. On the other hand, the right side of Equation 1 is derived dynamically as torque which is generated by the friction between the actuator and the ramp. Note that since the slider is supported near the disk surface by a thin cushion of air created by rotation of the disk, the friction force between slider and the air cushion is negligible compared with the friction between the tab on the point end of the suspension and the ramp.
With a reduction in the size of electronic computers, an attempt has been made to fabricate very thin hard disk drives. For example, in a very thin HDD with a thickness (in a paper surface depth direction of FIG. 1) of 9.5 mm or 12.5 mm, the thickness (height) of the spindle motor will also be thin. The height of a magnetic circuit which is incorporated into the motor interior becomes low and the effective length becomes short, and consequently, it becomes difficult to obtain a desired torque constant. The relation between the torque constant Kt [N m/A] and the counter electromotive force constant Ke [V sec/rad] becomes Kt=Ke. Taking numerical values for reference, Ke and Kv are 0.0089 and 0.23 for a HDD with a thickness of 12.5 mm and Ke and Kv are 0.0071 and 0.11 for a HDD with a thickness of 9.5 mm.
To compensate for disadvantages resulting from the aforementioned thinning of the HDD, VCM magnet 8 is provided with a protrusion 9, as shown in FIG. 5. This protrusion 9 is provided for increasing a magnetic flux density, thereby obtaining the force for driving a motor in cooperation with an iron piece 60 (see FIG. 6). However, in this case, the torque constant of the VCM magnet 8 becomes uneven depending on the rotational angle and therefore biasing force also becomes uneven. As a consequence, there is the disadvantage that positioning the actuator with the servo control becomes difficult particularly at the outer portion of a disk. Also, there is the disadvantage that a different made-to-order VCM magnet 8 must be prepared for each HDD, and consequently, the VCM magnet 8 is not suitable as a component which is attached to a HDD after fabrication of the HDD.
To compensate for disadvantages resulting from the aforementioned thinning of the HDD, the magnetic force of a lock magnet 70 (see FIG. 6) provided on the actuator is increased to strongly attract the iron piece 60. However, in this case, a problem arises during a load operation. When power is turned on, a large current has to flow in order to separate (or, to load) the actuator from the lock magnet 70. In many cases the separation becomes difficult because the value of current which flows through the coil and the torque constant of the VCM are limited due to a reduction in the size of the HDD. Also, even if the separation of the actuator from the lock magnet were successful, the actuator would forcibly be moving fast when separated. This causes an additional problem in that it becomes difficult to read out servo information from a disk in a short time. More specifically, servo control for positioning an actuator becomes difficult particularly at the outer portion of a disk.
An object of the present invention is to provide a mechanism which assists rotation of an actuator when the actuator assembly is removed to a ramp during an unload operation.
Another object of the present invention is to provide a mechanism which requires no excess separating force during a load operation.
Still another object of the present invention is to provide a mechanism which controls load and unload operations without making servo control for positioning an actuator difficult at the outer portion of a disk.